If it's organic (which, with a weed killer, it's really not), then yes.

Using synthetics (like Scott's), wait until temperatures drop well below 90 in your area. Read the bag to make sure it doesn't recommend a different temperature and if it does, follow that.

You'll probably want to cross-post this to the Lawn Care Forum where you'll get better advice on the subject.

Even on the other forum, the time to kill weeds with chemicals is in the spring. But the best time to prevent weeds is now by thickening up the grass. Overseed now and set your mower to the highest setting. Next year at this time you should have no weeds. It really is that simple.

Well what should I do ??Corn Gulten Meal cost $20.00 bucks for 50 lbs.I have 18,000 sf of St. Aug.
Or do I continue with a SBM,CSM,Alfafa pellet mix (which is working great). Here in Florida the weeds can overtake your grass quickly.
I am at major crossroad in the life of my lawn.
How bout it dchall what ya think !!!